I am having (weird) issues with XFS, in that open(...) on certain files
takes 45 seconds to return. After the file has been opened, the next
file in the same directory takes 45 seconds. If the file was recently
opened it returns immediately.

I thought this was a low level I/O issue, so copied the files in
question to a completely independent RAID array (separate LVM, RAID,
controllers, disks), but the problem remains.